Wrong ipv6 routes for local network addresses
Hi,
I'm not sure whether this is a problem of Network Manager itself or the Ubuntu flavored version. I had reported this to Ubuntu months ago, but nobody seems to care: https://bugs.launchpad.net/bugs/1936728
Some time ago I wondered (Ubuntu 20.04, NM 1.22.10-1ubuntu2.2, just found the bug to still exist in Lubuntu 21.10, NM 1.32.12-0ubuntu1) why my host-to-host traffic in my local network (just regular gigabit-switch with a internet router common on Germany, AVM FritzBox announcing ipv6 by RA and DHCP6) that sometimes the machines communicate full speed (GBit) when communicating
- over IPv4
- server to server
- or when other operating systems such as RASPBIAN are used,
but slow down once one of the Ubuntu Desktops (here: Lubuntu) is used. Then traffic over IPv6 (which is default) is drastically slower.
I found that Network Managers sets wrong IPv6 routes.
Usually (and e.g. on RASPBIAN oder other operating systems that's the case) the system should have a default route to the router and a link local route set to the interface, pretty much as with IPv4.
But those Ubuntu versions using the Network Manager instead set routes to the router, even for the site local and assigned ipv6 networks instead of link local routes. That's the reason why it slows down the traffice, since all traffic in my local network over IPv6 is not switched by the switch, but slowly routed by the internet router (fritz box), since routes point to it.
So the ipv6 routes are wrong, but might remain unnoticed in most cases, since they just slow down the traffic, but have it still running.
So where do these broken routes come from?
Are these set by upstream NetworkManager, or is this some ubuntu-specific flaw?
regards